The invention relates to collecting and focusing light from semiconductor light sources. Semiconductor light sources are presently under intensive research and development, and their field of application has been highly expanded. This is due to e.g. the small size, free controllability and high efficiency of the light sources.
Semiconductor lasers are used e.g. in communication, optical pumping of lasers, material machining, surgical operations, printers, and a variety of scientific devices. To provide high luminosity, it is possible to couple both several single diode lasers on top of each other or in parallel (stack and line lasers) and also line lasers on top of each other (matrix). A typical example of the system of several diode lasers is presented in U.S. Pat. No. 5,790,576 disclosing the coupling of a matrix structure, consisting of several lines of diode lasers, to an optical fibre by means of optical elements.
Diode lasers often produce an elliptical far-field whose maximum and minimum aperture values often differ greatly from each other. Elliptical (more generally: non-radial) fields are conventionally focused e.g. by means of cylinder lenses and/or diffraction gratings. A non-radial field refers to the far-field of a light source where the intensity distribution in the cross-sectional plane is not radial but for example elliptical or almost line-shaped, such as the far-field of the diode laser. The problem is often how to focus and conduct the light from several separate sources to an object in a simple and effective manner. As far as is known, it has not been possible to couple the light from several diode lasers to a light guide in a simple and effective manner and to focus it with the same device.
It is an aim of the invention to present a method by which it is possible to couple the light from several light sources producing a non-radial field into a light guide. In the method, any separate fibre system or lenses are not necessary to transfer light into the light guide, but the light sources can be attached directly to the end of the light guide. Depending on the shape of the light guide, the method can be used to couple light into a fibre or to focus light for other purposes.
This aim is attained by the method of the invention in such a way that the light guide has an at least partly curved cross-section in a direction perpendicular to the direction of propagation of the light, and light sources are coupled on the periphery of the light guide. When the main axes of the far-fields of the light sources are parallel to the tangent of the curve of the cross-section of the light guide, no collimation optics will be necessary, and light can be evenly spread into the light guide. The device of the invention, in turn, consists of a light guide whose outer surface is at least partly curved, and of non-radial light sources coupled on the periphery of the light guide. The coupling is preferably effected without optics between the light guide and the light sources in such a way that the main axis of the far-field is substantially parallel to the tangent of the outer surface of the light guide.
In view of the use and structure of the light guide, the invention has also other preferred embodiments which will be discussed below.